Telegraphic communication system with automatic answer back and alarm signals



June 28, 1949.

E: .E. KLEINSCHMIDT TELEGRAPHIC COMMUNICATION SYSTEM WITH AUTOMATIANSWER BACK AND ALARM SIGNALS 6 Sheets-Sheet 1 Filed Dec. 24, 1943TROUBLE 6 RENT 7 /2 INVENTOR. fizknemml June 9- E E. KLEINS'CHMIDT2,474,257

TELEGRAPHIC COMMUNICATION SYSTEM WITH AUTOMATIC ANSWER BACK AND ALARMSIGNALS Filed Dec. 24, 1943 6 Sheets-Sheet 2 A ORNEYJ' June 28, 1949. E.E. KLEINSCHMIDT TELEGRAPHIC COMMUNICATION SY STEM WITH AUTOMAT ANSWERBACK AND ALARM SIGNALS Filed Dec. 24, 1943 r 6 Sheets-Sheet 5 INVENTOR.MEf Wd/dfl mmmw I now NEYS.

June 28, 1949. E. E. KLEINSCHMIDT COMMUNICATION S 2,474,257 TICTELEGRAPHIC YSTEM WITH AUTOMA ANSWER BACK AND ALARM SIGNALS Filed Dec.24, 1943 6 Sheets-Sheet 4 M hm Av I 93 RAW fin own Q 5W @mg Ohm 7 v am#55 i If WNW , -.m kkiwzb lnljp 1?. RN w m l/wkm I N h ME mm Rm m v m I?w F, BEN 3m mwm D MWN \WN n+ U 0mm v I U MN m n. Nwm a. 8m 1 D MM j MWNN$N vmN wmm IN V EN TOR. mamflef A TT June 28, 1949. E. KLEINSCHMIDT 3TELEGRAPHIC COMMUNICATION SYSTEM WITH AUTOMATIC v ANSWER BACK AND ALARMSIGNALS Filed Dec. 24, 1945 6 Sheets-Sheet 5 W/ NEYS.

T E. E. KLEINSCHMIDT 2,474,257

COMMUNICATION SYSTEM WITH AUTOMATIC ANSWER BACK AND ALARM SIGNALS June28, 1949.

TELEGRAPHIC 6 Sheets-Sheet 6 Filed Dec. 24, 1943 Patented June 2 8, 1949UNITED STATES -ATENT OFFlC TELEGRAPHIC COMMUNICATION SYSTEM WITHAUTGMATIC ANSWER BACK AND ALARM SIGNALS Y My invention relates to asystem of telegraphic communication. While the preferred embodiment isespecially adapted for switching telegraph messages by a manuallyoperated switchboard, my invention also embodies features useful inautomatic switching systems, such for example as the control andsupervision of transmission circuits by means of automaticallytransmitted and received answerback signals; the feature of transmittingthe complete address of a message, that is, one containing more than onecode combination, to an automatic switch from an address transmitter inone operation; and the feature of maintaining two transmission circuitsconnected until an answerback. signal is received indicating the fullreception of a transmitted message at the ultimate receiving station, aswell as others.

Manually operated telegraph switchboards have heretofore been proposedand are used to some extent. These are, however, complicated and requirethe numbering of messages by the automatic transmission of successivenumbers over trunk circuits. To prevent loss of messages in such priorsystems a great amount of manual supervision is required and it has alsobeen necessary for the switchboard operator to read a printed orperforated tape to determine the destination of a message so that he mayswitch it to the proper circuits.

The elimination of the foregoing objectionable features of priorswitching systems is a primary object of my invention which I accomplishby providing a simplified system in which incoming lines are brought toa switchboard assembly in" a manner similar to a telephone switchboard.Each incoming line position has associated with it a series of lamps toindicate the ultimate destination of the message, a multiple contactjack, a start button, a signal lamp to indicate that a message is beingtransmitted and a signal lamp to give an alarm signal and means toretain the connection locked if the message has not been received or ifthere is a fault in the circuit or apparatus. Each jack is provided witha locking device to prevent the plug being withdrawn from the jackduring the transmission of a message, an ejecting device to disconnectthe plug when the transmitted message is correctly received and devicesto prevent connecting a plug to a busy circuit.

A further object of the invention is to provide a novel form ofperforated tape controlled transmitter with feelers and contacts thatare operative only when a message is waiting to be transmitted and whichthen close circuits to indicator lamps on the switchboard for giving theultimate destination address as Well as indicating whether the messageis an ordinary one or a deferred message or an urgent message. Thesecircuits from the transmitter may, in an automatic switching system, beconnected to control the selective switch mechanism.

Another object of the invention is to provide novel means forautomatically sending and receiving answer back signals for each messageor group of messages transmitted. In the preferred embodiment disclosedthe answerback signals are started at the receiving station undercontrol of the message end signals, and are transmitted to thetransmitting apparatus. After each message or group of messages has beentransmitted, transmission is stopped until the answerback signals arereceived whereupon the transmission is automatically restarted. If theanswer back signals are not correctly received, the circuits are heldlocked and a trouble indication given so that service operators maycorrect any trouble and retransmit the message wherein the faultoccurred.

A further object is to provide means to prevent registration of theanswerback signals in a transmitted message and to prevent the recordingin a message of the unshifted signal combination included in answerbackor service signals when the message includes figures or punctuationswhich are recorded in the shifted position of the message characterreceiver.

Another object is to automatically feed out accumulated blank signalcombinations at the transmitter between messages without transmittingsuch blanks over the circuit.

A still further object is to provide means to cancel the stoppage of themessage transmission function of answerback signals when, through somefault, these arrive in the body of a message.

Other objects will become apparent from the following description andclaims.

Referring to the drawings:

Figure 1 illustrates more or less diagrammatically a section of anassembled switchboard to be used in the preferred embodiment of myinvention;

Figure 2 illustrates diagrammatically one panel of an incoming circuitat the switchboard;

Figure 3 is an enlarged detail section on the line 3--3 of Figure 2,showing the construction of the jack and plug;

Figure 4 shows the'plug in its seat at the 'nel as will be describedlater. inserted in jack l4, spring l presses an insulated 3 switchboardand associated connections and locking device;

Figure 5 is a side elevation partially in section showing the essentialelements of a preferred form of tape transmitter used in the preferredembodiment of my invention;

Figure 5a is a similar view of certain of the elements not seen inFigure 5;

Figure 6 is a plan view with parts broken away of the mechanismillustrated in Figure 5;

Figure '7 is a fragmental side elevation of the stepping mechanismillustrated in Figure 6;

Figure 8 is a sectional view, along line of Figure 5;

Figure 9 shows the circuits from an incoming line to the jack and thevarious indicator lamps at the switchboard;

Figure 10 shows the apparatus and circuits at the transmitting terminalof a duplexed multiplex channel and connections to the switchboard;

Figure 11 shows the apparatus and circuits at the receiving terminal ofa duplexed multiplex channel and associated apparatus;

Figure 12 (Sheet 4) shows how the answerback method is applied toautomatic transmission systerns;

Figure 13 (Sheet 3) shows how the answerback method may be applied to asimplex telegraph system;

Figure 14; shows the answerba-ck control method applied to a duplextransmission system using relatively high frequency currents for theanswerback signals;

ing line; white indicator lamp 5 flashes during the transmission of amessage; red indicator lamp 5 flashes to indicate trouble when theanswerback message is not received; the first two rows and 8 of 5 lampseach indicate the address of the ultimate distributing point for themessage; a deferred message is indicated by the lamp and an urgentmessage is indicated by the lamp I I? all as will more fully hereinafterappear. The

circuit arrangements for lamps H and I2, as hereinafter pointed out, aresuch that when both are lighted at the same time, the indication is foran ordinary message. Start button 3 is operated to start transmission.Jack M is provided with an ejecting spring |5 which engaga flange N5 ofthe multiple contact plug 3 when the plug is inserted in jack M. Flangel6 rn'ust fit between guide walls It to insure proper insertion of theplug. Hook lever 26 is pivoted on a bracket 2| 7 and normally heldagainst the edge of opening 22 by a spring 23. Magnet 25 when energizedattracts hook lever 29 to release it from lug 26 of plug 3 thusPermitting spring Hi to eject plug 3 out of its socket. Contact pins 21,of which there are seven carried by plug 3, are connected through cable28 to circuits at an outgoing chan- When plug 3 is plunger 29 againstcontact springs 30 to close '4 them, and pins 21 each engage one ofseven contact springs 3|, only four springs 3| being shown in Figure 3.Contact springs 3| are connected to circuits of a local transmitter aswill be described later.

In Figure 4 plug 3 is shown resting in its socket on table portion 3| ofthe switchboard. When in this position, it depresses button 32 whichdisengages busy contacts 33 to hold the circuit of signal lamp 4normally open, as in Figure 15, vSheet l. A hook lever 34 pivotallymounted in a bracket 35 is normally held out of contact by l spring 38with ledge 38 forming a part of plug 3. A magnet 37 included in the busycircuit and mounted on bracket 35 attracts hook lever at to engage samewith ledge 36 when the trunk to which the plug is connected is busy, allas more fully hereinafter described.

Referring to Figures 5, 6, '7 and 8 which show the operating parts of apreferred tape transmitter used in my system, perforated tape 4|,movable beneath a perforated plate M3, is engaged by a row of five tapefeelers 42 for sensing messages and at times address signals. A row offive tape feelers 43 sense tape 4| for address signals. Deferred messagesignals are sensed by tape feeler i i, and tape feeler senses tape H forurgent message signals. All of the tape feelers are guided at theirupper ends in a plate 46, tape feelers 2,2 and 43 are guided at theirlower ends in a slotted plate 4'1, and tape feelers 44 and 45 areguidedin plate 48. The upper ends of the several tape feelers arereceived in the registering perforations of plate 40. Each tape feelerhas associated with it a contact lever; those associated with tapefeelers 42 are numbered 5|; those associated with the tape feelers 63are numbered 52; the one associated with tape ieeler 44 is numbered 53(Figure 5a); and the one associated with tape feeler 45 is numbered 5G.Contact members 5| are individually supported by insulated mountings onlevers 55 pivoted on a common bearing 56 carried on the supportingframework, not shown. Springs 57 act on levers 55 to urge the connectedtape feelers t2 upward and contact member 5| against a common contactbar 58. A bell crank armature lever 6| pivoted on a bearing 62 is shownattracted by transmitter operated magnet 63. A spring 34 retractsarmature lever 6| when magnet 53 is deenergized. The horizontal arm ofbell crank lever 6| has a terminal ball 65 which engages all of theledges 66 forming a part of tape feelers 52 so that, when magnet 63 isenergized as shown, all tape feelers 42 are withdrawn from engagementwith tape 4| and contact 5| is disengaged from contact bar 58. An upwardextension 61 (Figures 6 and 7) from hell crank lever 5| carries a pawl68 which is held in operative contact with ratchet H by spring 12. Astud 13 engages ledge Mforming a part of pawl 68, when magnet 63 is.deenergized and bell crank armature 6! moves to its retracted position.Detent lever .25 mounted on a bearing i5 is pressed against ratchet 1|by spring 71 to holdthe ratchet in the set position.

'Ratchet 'H' is fastened to a shaft 78 mounted in bearings 19 (Figure6). A feed wheel 8| also fastened to shaft 18 is equipped with pinprojections which engage the feed holes 82 of the trans- IOmitting tape4| to feed the tape step-bystep by the action of operating magnet 63.

Code holes 83 are perforated in the tape to correspond with the codecombinations required for each character to be transmitted. As thetapeisfed through the transmitter step-by-step during the transmissionof a message, tape feelers 42 either press against the tape 42 or passthrough a code hole 83 and permit the associated lever 55 to move itscontact member 5| against contact bar 58. The plate 40 is so positionedwith respect to tape 4! that those of the tape feelers 42 which engageblank tape, that is, where there are no code perforations, do not permitlever 55 to move a sufficient distance to allow contact lever 5| toengage contact bar 58. This operation of similar parts in standard tapetransmitters is well known.

Tape feelers 43, 44 and 45 are added to the standard tape transmittermechanism for the purpose of reading the address of a message and/or forcontrolling automatic switches when used. Tape feelers 43 areindividually associated with contact levers 84 which carry contacts 52and are pivoted on bearings 85 and pressed upward by individual springs86. All of the tape feelers 43 are normally held out of engagement withtape ll by a terminal bail 89 forming a part of armature lever 87 andpivoted on a bearing 88, by the action of spring 9|. Tape feeler 44associated with contact 53 and tape feeler 45 associated with contact 54are held in their normal lower position by a bail 92 operativelyconnected to bail 89. Levers 55 carry the contacts 53 and 54respectively and are actuated to circuit closing position by springs 98.It will be understood that the armature spring 9| is of greater strengththan the springs 86 and 98 to restrain action of the latter and normallymaintain contacts 52, 53 and 54 in open-circuit position. When theaddress of a message is to be recorded, magnet 93 is energized torelease tape feelers 43, 44 and 45 which thereupon assume positions inaccordance with perforations in the tape. Those passing through codeperforations in the tape permit corresponding levers 84 and 95 to beoperated to move contacts 52, 53 and 54 carried thereby into circuitclosing engagement with common bars 94 and 95. Magnet 93 remainsde-energized during message transmission.

The system herein disclosed contemplates that the receiving operator (atelegraph employee) when receiving a message from the public over thetelephone at a branch ofiice or over a subscriber teletype circuit willprefix each message when retransmitting it into the switching systemwith the code address of the ultimate central office distributing point,such code address to include special signals to indicate Whether themessage is an ordinary one, a deferred message, or an urgent message.Two letter code combinations will indicate the ultimate central olficeand the third combination will indicate the type of message. At the endof the message he adds a message end signal combination.

Switchboard connection from incoming line Referring now to Figure 9,Sheet 3, which shows the circuit arrangements associated with thetransmitter of an incoming line, transmitter I28 is constructed inaccordance with the showings of Figures 5, 6, 7, and 8, Sheet 2. Theparts shown in this view, which are numbered correspondingly, arecontrolled by perforated tape 4| in the manner previously explained. Theconnections of the transmitter, as well as the relay positions in thisview, are in the condition they will be in when a message is waiting tobe transmitted. At this time transfer relay |2| will be energized.Address magnet 93 Will be energized permitting tape feelers 43, 44 and45 to engage the message tape. Transmitter operating mag-"- net 53 willbe de-energized permitting tape feelers 42 to engage the message tape.

It is assumed that the perforations in the tape at that time will besuch as to set contacts 5|, 52, 53 and 54 in the positions shown inFigure 9. Current will pass from plus battery contact bar 58, throughthe connected contact members 5|, selecting relays I48, to correspondingarmature levers I 23 of transfer relay I2 contacts I59, wires I50 and toaddress lamps l, Wire I47, contacts I41, and negative battery. Currentwill also pass from plus battery, common bar to the connected contactmembers 52 and lamps in group 8, contacts I41, to negative battery, andto contact member 53, lamp II, contacts IN, to negative battery. Inaccordance with the connection shown the third and fourth lamp in groupi, the first, third, and fifth lamp in group 8, and lamp 5 I will belighted indicating on the address lamps that the message waiting is adeferred one, destined for NY which are the symbols for New York. Thisaddress and type of message will be read by the switchboard operator whothen inserts a plug 3 connected to a New York trunk in a jack I4connected to the waiting message, or if the lines are busy and since thewaiting message is a deferred one, inserts a plug 3 that is connected tostorage apparatus especially provided for deferred messages. The storageapparatus may be located at the New York trunks or may be connected tospecial switchboard positions.

Transmission from incoming circuit Before describing the operation ofrelays, etc, when a plug 3 is connected to the circuit, I will give ageneral description of the condition of the circuits at the time of awaiting message, that is, when the address lamps are lighted. Only relay|2| and holding coil I22 of relay I26 are energized at this time. Relay|2| was energized by the operation of the message end signal and relay|2|; was energized by the answerback signal. Battery |3i5 is at thistime charging condenser I31 through contacts I38. Holding coil I22 ofrelay I25, holding coil I43 of relay I44 and holding coil 54E of relayI45 are composed of windings of a comparatively small number of turns,insufficient when energized to attract the armatures of the relays butsufficient to hold the armatures attracted after the relays are operatedby their respective operating coils.

When a switchboard operator inserts a plug 3 in jack I4 to transmit thewaiting message, sixth pulse impulses from the trunk to which plug 3 isconnected will periodically pass over wire I4I from positive battery'atthe trunk through relay I42, holding coil I43 of relay I44 and negativebattery. Start key I3 is now depressed closing contact I40 to prepare acircuit for the discharge of condenser I31 which is closed throughoperating coil I44 of relay I44 when contacts it? are closed by a sixthpulse arriving on wire 34E Energized holding coil I43 holds relay I44operated during the sixth pulse. The pulse from start key I3, when thatis depressed, is a momentary condenser discharge, so that if the key isheld down during the transmission of one or two letters, nothing occurs.Contacts I5I and hit of relay I44 will be opened during this sixth pulseinterval. Contacts I5I open the holding circuit for relays |2| and I26.Contacts I35 open the sixth pulse circuit wire I4 I to relay E65 andmagnet 63. Relay I26 when released opens contacts I41 disconnectingnegative battery from the address lamps and closes contacts I25 whichclose a r-rigs? a circuit from positive battery through holding coil N6of relay I45, resistance I68 and negative battery. Relay I2I whenreleased by the opening of contacts II opens contacts I28 in circuitwith address magnet 93 which releases armature 81, and tape feelers 43,44' and 45 are released from engagement with tape M by the action ofspring 9I (Figure 5, Sheet 2). Selected contacts 5| will however remainin contact with common bar 58. The sixth pulse now on wire I4I cannot atthis time pass to relay I65 and transmitter operating magnet 63 overwire I41 and close contacts I32 of relay I2I, since contacts I39 ofrelay I44 are open during the first sixth pulse interval. Selectedcontacts 5I will therefore remain in the set position after the firstsixth pulse is received on wire MI and the first code combination intape 4I, forming a part of the address of the message, will betransmitted over relays I48, contacts I52, wires I52, jack I4, plug 3,and through cable 28 to a bank of relays at the connected trunk. Thesecond and following pulses passing over the sixth pulse circuit MI andNH will not operate relay I44 but operate relay I65 and magnet 63through contacts I39 of relay I44, wire I4I', contacts I32 of relay I2I,and contact I33 of relay I45 to relay I65 and transmitter operatingmagnet 63 to negative battery, and step transmitting mechanism for tape4I- through transmitter I20. Relay I42 will also be operated but willclose no circuits other than through contacts I54, lighting white lamp 5with every sixth pulse through closed contacts I53 of relay I45, and I30of relay I2I, thus giving the switchboard operator an indication thatthe message is being transmitted.

The transmission of the full address and message continues until themessage and signal combination in tape 4! reaches feeler pins 42. Themessage end signal combinations used for the purpose of this descriptionof the invention are the code combination commonly used for carriagereturn comprising three spacing, one marking and one spacing signalsfollowed by a blank code combination, that is, one containing fivespacing signals. The carriage return code combination always sets relaysI40 to close series contacts I55, closing a circuit from positivebattery, contacts i64 of relayI65, wire I64, contacts I55, relay I56 tonegative battery. Relay I65 opens this circuit during the sixth pulseinterval to prevent relays I48 getting false impulses during the contactsetting period. Relay I56 is suiiiciently slow release to hold itsarmatures attracted over the sixth pulse interval. The closing ofcontacts I58'and I35 by relay I56andthe opening of contacts I66 willhave no effect since the connected circuits are open at other points atthis time. When however a blank code combination immediately follows acarriagereturn combination, all'the relays $48 remain de energized andseries contacts I57 of relays I48 are closed before relay I56 releasesits armatures and current now passes through contacts 158, operatingcoil I56 of relay I45, relay I56 to nega tive battery. Relay I45 isoperated and h'eld so by the energized holding coil I46, untilthemswer-back signal is received. Contacts I6I! of relay I45 close acircuit over wire I60 from positive battery through relay I2I, holdingcoil I22 of relay I26, contacts I5I to negative battery; Relay I2!operates to move armatures I23 from contacts I52 to contacts I50transferring the circuits from contacts 5I'- to the addres's lam s I.Relay I2I- closes contacts-I2Iwhich close a;

self lockin'g circuit that remains closed until start key I3 isdepressed. Relay I opens contacts I33 and closes contacts I34transferring the circuit of relay I and magnet 63 from the'outgoingtrunk sixth pulse on wires I41 and MP to an auto-pulsing circuit I12through closed contacts I35." The auto-pulses periodically energizerelay I 65 and magnet 63, which impart step movements to the tape 4Iover feeler pins 42 until a code perforation is reached. One or more ofthe relays I46 are then energized and the circuit through seriescontacts I51 interrupted, whereupon relay I56 is released and contactsI35 opened disconnecting the auto-pulsing circuit H2 and leavingtransmitter I20 at rest, with feeler pins 42 pressed against tape 4i.Contacts I66, relay I56 and closed contacts I of relay I45 close acircuit through red trouble lamp 6 which flashes by the periodic closingof contacts I54 of relay I42 until the answerback signal is received.Contacts I29 of relay I2I close to prepare the answerback circuit fromwire I'II. Contacts I28 of relay I2I close to prepare the circuit foraddress magnet 93. Contacts I30 of relay I2I open the circuit for whitelamp 5. Contacts I32 of relay I2I open the sixth pulse circuit to relayI65 and magnet 63. Under normal conditions when no faults exist ineither the circuits or apparatus, the answerback signal is received onwire I'II within one second after the message end signal is transmittedfrom contacts 5i. The answerback signal when received passes throughoperating coil I6I of relay I25 and disconnect magnet 25 over wireI'II'. Relay I26 when operated remains so until key I3 is depressed tostart a new message. Magnet 25 releases plug 3, whereupon spring I5ejects it from jack I4. Relay I26 opens contacts I25 de-energizingholding coil I46 and relay I45 is released. Contacts I4! of relay I26connect negative battery to address lamps I, 8, II and I2. When relayI45 is released, it closes the circuit to address magnet 63 throughcontacts I73, wire I13 and closed contacts I28 of relay l2I. Acombination of lamps II and I2 and certain of the lamps in groups 7 and8 are now lighted in accordance with the code combinations of theaddress characters in the next waiting message. As before stated relaysI26 and I2I remain operated. The switchboard operator now reads theaddress lamps for the destination of the message and inserts in jack I4a plug 3 that is connected to an outgoing trunk that will carry thewaiting message to its destination after which he depresses the key 13to start transmission.

I If an answerback signal is not received on wire I 7!, red trouble lamp6 will flash and plug 3 will remain connected to jack I4. When thisoccurs the switchboard operator summons a service attendant whocommunicates with a service attendant at the receiving station. When thefault islocated and repaired, transmission is re started.

Contacts I29 of relay I2I, which are open during message transmission,are provided to prevent an answerback impulse on wire III from operatingrelay I26 or disconnecting magnet 25 at any time other than after amessage has been transmitted.

Preventing duplicate switchboard connections For a switchboardarrangement where a series of incoming transmitter circuits, as shown inFigure 9, Sheet 3, will have difierent switchboard positions eachconnected to a jack I4 and attended by individual operators; I'providemeans to make impossible the connection of more than one plu 3 to thesame waiting message in the following manner: Referring to Sheet 1,Figures 3 and 16, each jack of a group connected to the same transmitterI20 is provided with a pair of contact springs 30 which are closed by aplunger 23 when a plug 3 is inserted in a jack I4. Each set of contacts30 in such group is connected through a limiting resistance I02 to amultiple circuit I33 and positve battery. Relays I04, one for each jack,are connected in series circuit I05, to negative battery and to circuitI03 as shown in Figure 16. Relays I04 are wound so that current passingthrough one limiting resistance I02 will not operate them. When howevertwo contacts 30 are closed at the same time current will pass throughtwo limitin resistances at the same time and sufiicient current willflow through series circuit I05 to operate all relays E04 which closecontacts I06 (Figure 9) to close a circuit through disconnect magnet 25which will prevent the locking in of any of the inserted plugs 3. Whenall of the plugs 3 except one are withdrawn the latter will lock in,whereupon the operator depresses start key I3 extinguishing all addresslamps. Contacts I01 operated by relay I26, which is de-energized duringmessage transmission, are provided to prevent closing of the circuit todisconnect magnet 25 during message transmission.

Connection to multiplex system Figure 10, Sheet 4, shows the sendingsection 2E0 and the receiving section 220 of one duplex multiplexchannel of a multiplex distributor 200 and the connections associatedtherewith. The five transmitting wires from plug 3 are connected to fivetransmitting relays numbered 20I to 205 which are normally de-energizedclosin their upper contacts to transmit negative impulses throughbattery 226 from ground 22I to transmitting segments 222 of themultiplex distributor which during transmission are connected byrotating brush 223 to ring 224 and outgoing line 325. During thetransmission of message characters one or more or relays 20I to 205 willbe energized and move their armatures against the lower contact totransmit impulses from positive battery 221. Ring 230 connected topositive battery is connected by brush 23I to sixth pulse segment 232after brush 223 has passed over the transmitting segments 222. Ring 231is connected to contacts 233 of receiving relay 239 and by brush 242 tothe receiving segments 243. Ring 233 connected to positive battery isconnected by brush 234 to segment 228, receiving sixth pulse segment 235and relay break segment 235 after brush 242 leaves receiving segments243. As is well known in the operation of multiplex distributors, thebrushes 223, 23I, 234, and 242 revolve together as one unit and insynchronism with similar brushes 423, 43!, 434 and 442 shown in Figure11 forming part of a like multiplex distributor 483 at the distant endof the duplex circuit, and it is assumed that impulses from groundconnection 22! will pass over line 225 to receiving relay 439. Thearrangements of relays and circuits in Figure 11 are the same as inFigure and bear the same numbers except that these are in the 400 and500 groups.

The circuit arrangements and relays in Figures 10 and 11, Sheets 4 and5, are shown in the normal unoperated position, and it is assumed thatthe brushes 222, 223, 23I, 234 and 242 are rotating and in synchronismwith brushes 422, 423, 43I

10 and 442 at the distant end of the line, and that a switchboardoperator is ready to insert plug 3 connected to relays 20I to 205 in ajack I4 connected to a waiting message. When the plug is insertedseveral sixth pulse impulses may be transmitted from positive batteryring 230, segment 232 and wire 232' to wire MI and relay I42, Figure 9.At Figure 10 these impulses will pass through coils 321 and 323 of sixthpulse control relay 330 in opposite directions and relay 330 istherefore not operated at this time or during message transmission, thecircuit from segment 232 to wire I4I being from positive battery ring233, segment 232, wire 232' and in a divided circuit over wire 320' andcontact 320 and over contacts 326 through coils 328 and 321 to wire I4I.After inserting plug 3, the switchboard operator depresses start key I3which starts the sending of message impulses from the transmitter I20 inthe manner previously explained. These message impulses are received onrelays 20I to 235 which connect either positive or negative battery tothe transmitting segments in ring 222. As the distributor brushesrevolve corresponding impulses are transmitted to line 225 in a mannerwell known in the art. Brushes 23I connect segment 232 to positivebattery after the transmission of each group of character impulses andtransmit a sixth pulse impulse over a wire I4I to the apparatus inFigure 9 operating the transmitter i23 periodically in the mannerpreviously explained. At the end of the message, vmessage end signalcombinations are transmitted comprising a carriage return combination ofthree negative, one positive, and one negative impulses followed by ablank combination of all negative impulses. Transmission fromtransmitter I20, Figure 9 will then stop. The multiplex brushes,however, continue to rotate sending blank code combinations since all ofthe relays 20H to 205 will remain de-energized.

Multiplex distributor 200, Figure 10, Sheet 4, is connected to multiplexdistributor 400, Figure 11, Sheet 5, by line 225 and, as is well knownin duplex operation, signals from the sending section 2m operate relay439 and signals from the sending section 4I0 operate relay 239. When amessage is transmitted from sending section 2I0, relay 433 operatescontacts 438 to open and close a circuit from ground and battery 46I,contact 433, ring 431, brushes 442, segments 443, selecting magnets 460to ground, also through relays 413 to 414 to ground. Relays 410 to 414lock up when operated through contacts 415,- the circuit a being fromground, coil of a relay 430 to 414, contacts 415, contacts 416 of relay411 to battery and ground 418. During each rotation of brushes 442 and434, magnets 460 and relays 410 to 414 will be energized in accordancewith the code combination received. After a code combination of impulsesis received, brush 434 connects segment 435 to ring 433 closing acircuit from plus battery through perforator or printer operating magnet432 over wires 453 through parallel connected contacts 503 and 484,series contacts 435, and negative battery 463'. Magnet 432 will recordthe code combination selected by magnets 46% in the record medium of thereceiving apparatus. After brush 434 has passed over segment 43% itcontacts with. segment 436 to close the circuit through break relay 411opening contact 415 and the locking circuits for relays 410 to 414 whichthereupon assume their unoperated positions. Brushes 434 connect ring433 to segment 11 428 at the same time that brushes 442 contact with thefifth selectin segment'in group 443.

Reception of message codecombinations continues until the end of messagecode combinations are received which are recorded in the followingmanner: Relays 410 to 414 operate as selecting relays to detectthe'unshift, shift, letter J, carriage return and blank codecombinations, and their contacts are connected in series as to therelays in the manner shown. When at the end of a message the carriagereturn and blank code combinations are received in succession, a circuitis first closed by relays 410 to 414 through the carriage return row ofseries contacts 450, closing a circuit from battery 418, contacts 416,holding coil 45I of relay 452, contacts 453 which are closed whenbrushes 434 contact with segment 428 to'energize relay 452 over wire428, series contacts 450, slow release relay 454 and ground. Thefollowing blank code combination closes series contacts 455 closing acircuit from battery 418, contacts 415, coil 454, closed contacts 453,series contacts 455, closed contacts 455, contacts 459, operating coil4-51, of answerback relay 453, relay 454, and ground. Relay 458 isoperated and locks up by closing a circuit from negative battery throughnumbering stamp 515, holding coil SIS, of relay 458, contacts |4, relay5l1, contacts 518, wire 5H], and positive battery. When relay'458operates it closes self-locking contacts 514 before opening contacts 459which are in its operating circuit. Contacts 459 open the circuit fromblank series contacts 455 to slow release relay 454 allowing it to opencontacts 456. Numbering stamp 545 prints a'number on the message justreceived. It will be understood that an-identifying number is alsoprinted on the message at the receiving section 220 of the apparatusshown in Figure '10, when a'blank code combination is received, byclosing a similar circuit through holding coil 316 of relay 258' andnumbering stamp M5, in themanner just described. Relay 5| 1 is operatedto start the transmission of an answerback message to transmittingchannel 2 I 0 as will be described later.

The function of relay 452 is to hold the battery circuit'to seriescontacts 516,490, 513, 450 and 455, open while they are being set byrelays 410 to 414. Relay 452 is energized at the time brushes 442pass'over the fifth segment in group 443. If at that time any of theseries contacts operated by relays 416 to 414 close a' circuit, relay452 maintains the circuit closed by closing a locking circuit throughcontacts 453 and holding coil- 45] energizeduntil contacts 416 areopened.

Transmission of answerbacksiynals When an answerbackmessage is startedover a channel while a telegraph message is being transmitted,transmission of the telegraph message is stopped'and an answerbackmessage consisting of shift, J ,and unshift code combinations istransmitted from an answerback transmitter andthereaiter telegraphmessage transmission is resumed.

The automatic transmission of the answerback message from thesendingsection of channel 4!!! operates as follows: During thetransmission of a telegraph'message selectiveimpulses are received froma transmitter I over a plug 3 on relays 484 to 455 as previouslyexplained in connection with thesending channel 2|iland sixth pulseimpulses are transmitted from segment 432, wire 432 thr0ugh contacts 526of relay .530, coil 521,

andethrough wire 520', contacts 520, wire 528',

coil. 528 to wire I41. Current passes through coils 521 and 525' inopposite directions neutralizin the magnetic effect and sixth pulsecontrol relay 53 i is not operated by the sixth pulseduringmestransmission. When, however, relay 511 is operated by ananswerback signal from receiving channel 424, and contact 520 opened, nocurrent can pass to coil 528. A .sixth'v pulse coming through at this.time or later will operate relay 53!] closing contacts 532 andthereafter opening contacts 525' closing a holding circuit through coil521 from plus battery 524, contacts. 532, coil 521, wire I44, andtransmitteroperating magnet 63, Figure 9, Sheet 3, over contacts aspreviously explained, holding magnet 63 energized until contacts 532 ofrelay 533 are again opened which occurs after the answerback message istransmitted. It is to be noted here that when magnet 63 is energized allof the contacts'numbered 51 are out of engagement with common bar 58'andtherefore no current passes to relays 40l to 405 from this source atthis time.

The sixth pulse just described also passes through answerback steppingmagnet 533 over closed contacts 522 operating same to step'ratchet 536the space of one tooth. When relay 5l1 is operated during a sixth pulseinterval and only a part of the sixth pulse is received, relay 53!] willbe operated as explained and asupplemental circuit over wires 533' isclosed to 'magnet 533 through contact 550 of relay 530 and contacts 556of answerback apparatus 525 and closed contacts 52! of relay 511 toinsure its operation. Contacts 555 are again openedwhen contact 'lever555 leaves the rise on cam 548 at the end of the first operation ofarmature 534 ofstepping magnet 533. Magnet 533 ofanswerback instrument525, when operated, attracts armature 534 which is retracted by spring534'. A pawl 535 attached to armature 534 engages an eight toothedratchet 538 to step same the space of-one tooth in each operation of thearmature. 'A detent 531 operatedby spring 531 is provided to hold theratchet in the stepped position. 'Ratchet' 536 and seven camsnumbered-542 to 548 are fixed to a shaft 538 and rotate together as'oneunit. Cams 542 to 545 are provided with notches arranged so that duringthe successive stepping movements by the operation of armature 534,contact levers 55!] which cooperate with cams 542 to 545 will be set inpositions to successively set up connections for the shift, J, unshiftand blank code combinations. Contactlevers 550 are'connected by wires55! to transmitting relays 4! to 405 as shown, and engage contactsconnected to plus battery 552 when operated by a rise in the associatedcam. Normally they are resting in notches of their associated cams asshown. At the first operation of armature 534 during the transmission ofan answerback message, cams 542 to 548 are moved the distance of onestep operating the selected contactlevers 550 to transmit plus batterycurrent to the connected transmitting relays 43! to 405 over wires 55!setting them to transmit the shift code combination over transmittingsegments 422, brushes .423, ring 424, line 225 from batteries 426', 421,and ground 42!. After brushes 423 have passed over the segments 422,brush 43! will connect sixth pulse segment 432 .to plus battery throughring .430. This, the second sixth pulse impulse will .pass'throughcontacts 522, and magnet 533 again operates armature 534 to step theratchet 536 intothenext position which will cause cams 542 to 545- to.setv thescontact levers 553 into a. position .to send the -letter.J,.code

combination to line 225 in the manner as previously explained. The nextsixth pulse steps ratchet wheel 536 to set the contact levers 550 in amanner to transmit the unshift code combination to line 22 5. The nextsixth pulse again energizes magnet 533 as previously explained, settingthe ratchet wheel 536 in the fourth position which is the same as shownin the drawing except that cams 542 to 548 have moved one hundred andeighty degrees. All of the contact levers 550 will now open theconnection to plus battery 552. Contact lever 555 is operated by cam 548to close contacts 556 while contact lever 551 drops into a notch in cam541 to open contacts E9. As will be noted this occurs at the end of thedownward movement of lever 534, when the part 539 thereof, at itsextreme operated position, opens contacts 5|8. The simultaneous openingof contacts 5 i 3 and 5 I 9 opens the holding circuit through relay 55?,holding coil 5H6 of answerback relay 458, and numbering stamp Bill,which thereupon assume their unoperated positions. When relay 5I1 isde-energized contacts SH and 522 are opened and 520 closed so that thesiXth pulse impulse now passes through coils 521 and 528 of relay 5353in opposite directions neutralizing the magnetic effect, whereupon relay535 releases its armatures to the position shown in the drawing.Transmitter operating magnet 63, Figure 9, is now disconnected fromcontinuous plus battery current by the opening of contacts 532 so thatupon the cessation of operation of this sixth pulse impulse transmittermagnet 63 is deenergized to set the transmitter contacts for the nextletter of the wating telegram and message transmission continues in thenormal manner. The sixth pulse circuit MI is connected to negativebattery through resistance 2 l2 so that sixth pulse impulses fromsegment 232 will have a complete circuit over wires 232 and I4! andtransmission from answerback transmitter 325 will function correctlywhen plug 3 of the channel is not connected and no messages are beingtransmitted.

Reception of answerbaclc signals The answerback message just transmittedis received on receiving section 220 of distributor 200. The first shiftcode combination will be recorded on selecting magnets 250 and onselecting relays 213 to 214, which close a circuit through seriescontacts 235, from positive battery 218, holding coil 25H, closedcontacts 253, series contacts 290, operating coil 239 of relay 252, coil293 of relay 293, and negative battery. Relay 292 operates, closing aself-locking circuit through contacts 291 from positive battery,contacts 295 of relay 38!, holding coil 296, contacts 291, holding coil298 of relay 380, and negative battery. Holding coil 293 of relay 300 iscomposed of a few windings so that when the circuit to it is closed, itwill not energize relay 300 sufficiently to attract armature 352 butwill hold same attracted when relay 303 is operated by current passingthrough coil 355. Contacts 303 open when relay 294- is energized.Contacts 304 of relay 292 close a trifle later so that no current willpass through coil 306 of relay 300 at this time. Relay 292 also closescontacts 308.

The following J combination will close series contacts 310 closing acircuit from battery 213 through contacts 315, contacts 338, operatingcoil 31! of relay 312, relay 315, wire Ill to disconnect magnet 25, andrelay I25, Figure 9 releasing connected plug 3. Relay 315 remainsenergized circuits 263 to perforator or printer operating magnet 252,will be open when brushes 235 connect positive battery to sixth pulsesegment 235 and the letter J set up on selector magnets 260 willtherefore not be recorded. It is to be noted that while the letter Janswerback combination is not recorded on either the printer orperforator it does however transmit an answcrback signal to theassociated sending channel.

The following unshift combination is received on series contacts 316 ofrelays 213 to 215 which close a circuit from battery 213, closedcontacts 253, series contacts 315, relay 333 and ground. Relay 385operates to close contacts 301 which connect battery 335 in series withcondenser 383, charging the latter. When relay ill opens the holdingcircuit at contacts 213 for relays 210 to 215, and relay 252, relay 330will be ole-energized and close contacts 330 allowing condenser 333 todischarge through relay 33l which then operates to open contacts 235 totake plus battery current off the holding circuits to relays 292, 333,and 372, thus restoring relays 292, 353 and 312 to their normalunoperated condition.

Cancelling unshift signal combinations When, before the reception of theanswerbacl: message, the printer or perforator is in the shiftedposition, that is, recording figures or punctuations, and an answerbackmessage comes through at this time, it will pass through circuits andrelays so arranged that the unshift code combination forming a part ofthe answerback message will not be recorded on either the printer orperforator. These circuits and relays operate in the following manner.

A shift combination received on selecting relays 2m to 215 operates aspreviously explained to energize and lock up relay 292 and energizeholding coil 238 of relay 300. Relay 2 94 will also operate sincecontacts 303 open before contacts 3% close. If an answerback messagearrives while relay 292 is locked up by a previously received shift codecombination, the first code coinbination of the answerback message,which is a shift combination, will be received on selecting relay are to213, and current will again pass through coil 23! of relay 232 andthrough coil 293 of relay 235. However, since contacts 355 Were closedby the preceding shift combination, current will also pass through coil331 and operating coil 305 of relay 3% through contacts 335. Current nowflows through coils 293 and 337 in opposite directions, neutralizing themagnetic efiect and contacts 333 remain closed to permit current to flowthrough operating coil 305 of.

relay 300 which remains operated after this second shift codecombination is received, due to the energization of holding coil 253. henext code combination (letter J) will. close contacts 310, energizingrelays M12 and 3Y5 which operate to send an answerbach signal to theapparatus in Figure 9 connected to the associated sending channel overdisconnect wire W i. Relay 312 When operated locks up through contacts 313 and opens contact 235. The last code combination (unshift) closescontacts 335 to operate re lay 380 which closes contacts 331 to chargecondenser 383. The circuit to negative battery 253 from printer orperforator operating magnet 252 over wires 253 is now open at contacts232, and

284 so that when brush 234 contacts with segment 235 no current willflow to magnet 252 and the unshift code combination just received onrelays 278 to 2' will not be registered on either the printer orperforator and therefore the character receiving apparatus remains inthe shifted position. When relay 21? opens break contacts 213, relay 339is released opening contacts 3t! and closing contacts 380 which connectcondenser 333 in circuit with relay 3%! to discharge therethrough. Relay38! opens contacts 2% to release relays 29 2 and 372. It is to be notedthat the circuit arrangement just described is effective to preventrecording of the unshift combination on printer or perforating receivingapparatus only when this receiving apparatus is in the shifted positionbefore the reception of an answerback or service message.

Service signals It is the practice in types of well known multiplex andsimplex telegraph systems to provide an apparatus commonly known as anauto control to transmit service messages which are usually received ona bell at the character receiving apparatus. Such service messagesconsist of one or more groups of shift, letter J and unshift codecombinations. It is contemplated that such service messages may be usedin the system herein described for communication between service men incorrecting faults. When the auto control apparatus is to be used in thismanner, the service men first operate the switch 39! at their respectivestations to open the disconnect circuit and disable relays 312 ,and 315.Letter J code combinations will then be received on the bell at thecharacter receiving apparatus and no impulses will pass to disconnectwire I'll.

Control of trunk: circuits by answerback signals The method ofcheckingthe reception of a transmitted message over a circuit bystopping transmission from a sending station after a message has beensent, under control of a transmitted message end signal and returning ananswerback signal to the sending station from the receiving station torestart transmission, under control of a. received message end signal,and further to operate an alarm at the sending station if an answerbacksignal is not received after the message end signal is transmitted, canbe applied to various types of transmission systems to check the correctoperation thereof. I have shown and described an application of thismethod to a system for switching telegraph messages to their points ofdestination. I will now describe how the above stated method is appliedto automatic transmission circuits. The apparatus in Figure 12, Sheet 4,now to be described is shown connected to the apparatus of Figure 10 bydotted lines. When the two are connected plug 3 is not used. Referringto Figure 12, H is a type of perforated tape transmitter commonly usedin permutation code message transmission of which only the transmittingcontacts Hi, common con-. tact bar I I2 and operating magnet l i3 areshown. Common bar 1 I2 is connected to positive battery, contacts iiiare individually connected through relays H5, H6, Hl, H8, and H9 torelays 21, 282, 2%, 2M, and 205, then to a common wire 2% connected tonegative battery. All of the apparatus is shown in the normal unoperatedposition. Brushes 223, 231, 234, and 242 of distributor 280 arerevolving in synchronism with brushes G23, 53!, 434, and 442 of distantdis-.

tributor 400 which is connected to distributor-200- byline circuit 225.As brushes 231 pass over sixth pulse contact 232 an impulse istransmitted from positive battery to relay H4 and transmitter operatingmagnet H3 and negative battery over contacts H5 of relay I83, wire MI,and contacts and relays in Figure 10 as previously explained. Magnet H3will step the transmitting tape forward and contacts HI will be set inaccordance with perforations in the tape on each de-energization ofmagnet H3. When the message end indication comprising a carriage returncode combination followed by a blank code combination is reached, thecarriage return code combination will set relays H5 to H9 to close theseries connected contacts [T6 to close a circuit from plus batterycontacts Ill of relay H 3, series contacts ll'u, relay I18, to negativebattery. Relay l'i'8 is suiiciently slow release to hold its contactsclosed over the sixth pulse interval. The following blank codecombination will set relays H5 to H9 to close series connected contactsHill closing a circuit from positive battery, contacts HT, seriescontacts i883, closed contacts l8! of relay H5, contacts 182 of relayI85, relay I83, relay HS and negative battery. Relay l83 will open thesixth pulse circuit at contacts H5. Contacts i l I remain set inaccordance with the blank code combination in the transmitting tape andrelays H5 to H9 maintain series contacts 180 closed. Furthertransmission from tape transmitter i it is now stopped.

The message end code combinations are transmitted to the distant stationwhere they are interpreted, and operate apparatus to start an answerbackmessage in the same manner as previously described. The answerbackmessage when received sends an impulse on wire ill from positive batteryto relay I85 and negative battery. Relay i823 thereupon opens contactsI82 releasing relays 18S and H8. Contacts H5 are now closed so that thenext sixth pulse can operate transmitter operating magnet H3 andtransmission of messages resumes in the normal manner until anothermessage end code combination reaches relays H5 to H9. Relay H4 opens thebattery circuit to series contacts H6 and so that during the changing ofcontact positions of contacts Hl any false closing of series circuits H6and I80 will have no effect.

Under normal conditions, when a message end signal is transmitted andmessage transmission stopped, an answerback signal is received at thesending station within one second of time. An alarm is operated, if, dueto the non-reception of a message, or some other fault, the answerbackmessage is not received. For this purpose I have provided aninterpreting device consisting of normally energized slow release relayl8! connected with relay 183 at contacts 375', and an alarm circuit I83including alarm apparatus H39. During the interval between thetransmission of a message end signal and the returning of an answerbacksignal, relay contacts H5 are open and no current passes to slow releaserelay lB'l. If an answerback signal is received, the circuit to relay5B! is again closed before its armature is released. If, however, noanswerback signal is received, relay I81 releases its armature closingcontacts I96 operating the alarm M9 to call service attendants who willcorrect whatever fault existed and retransmit any messages not receivedat the receiving station.

The carriage return and blank message end signal combinations as well asthe shift, J, and

unshift code combinations which as shown in Figures 10 and 11 arereceived by selecting relays, can of course be received through contactsapplied to and operated by the selections of the receiving printer orperforator. If this is done, the message end and answerback codecombinations will serve to test the correct operation of the receivingapparatus.

An important feature of this invention is that all of the signalcombinations used to perform service functions are also used in normalmessage transmission and no additional service function codecombinations need be provided for this purpose.

Answerbaclc control of simplex circuits A further adaptation of themethod of controlling the transmission of messages by an answerbacksignal from the distant receiving apparatus as applied to a simpletransmitting circuit is shown in Figure 13, Sheet 3, in which a standardpermutation code printer is represented by its operating magnet 660. Astandard tape transmitter 66! provided with transmitting contacts 862and an operating magnet 663 is controlled by contacts 6% in a mannerwell known in the art. The transmitter contacts connect selectivelyunder control of a perforated tape to a common bar 605 connected tobattery 666 and ground 607. A line Eli connects the transmittingapparatus and printer magnet 600 to a receiving printer or perforatoroperating magnet 6l2 and to ground 6l3 through contacts 614 by wire Mforming a normally closed circuit in accordance with the normal practiceof setting up a standard simplex transmitting circuit for permutationcode startstop printers except that the contacts 6l4 are included in thecircuit. Code combinations of signals from transmitter 6M operatemagnets till! and M2 to control the starting and stopping as well as theselecting operations of either printer or perforator, or apparatus toboth print and perforate the received message on the tape, in accordancewith standard practice and in a manner well known in the art.

To control the operation of the transmitting apparatus from thereceiving apparatus I have provided the following circuit arrangements;contacts 626, 62l and 622 are operated by the code selections of aprinter which may be performed by the operation of a pull bar or anyother operative device that is set in accordance with the received codecombinations of signals. Contacts 620 are closed on the reception of acarriage return code combination comprising three spacing, one markingand one spacing signals. Contacts 621 are closed on the reception ofblank code combination comprising five spacing signals. Contacts 622 areopened on the reception of a line feed code combination comprising onespacing, one marking and three spacing signals. At the distant receivingapparatus contacts 640 and 64! are likewise operated by the receivingprinter or perforator. Contacts 6 36 close on the reception of acarriage return code combination and contacts 64! close on the receptionof a blank code combination.

As in the previously described arrangements,

gize slow release relay 625 which closes contacts 626. These are heldclosed for a short interval after contacts 620 open due to the slowrelease feature of this relay. When the next following code combinationcloses contacts 621, relay 636 is energized and locks up over closedcontacts 63! and 622. It also opens contacts 632 and 633. Contacts 632open the circuit to transmitter operating magnet 603 leaving thetransmitter in the set position with the five transmitting contactsopen, thus stopping transmission.

At the distant station contacts 646 and 6M operate in the same manner ascontacts 620 and 62!, first energizing relay 645 and then relay 646through closed contacts 641. Relay 646 when operated closes contacts 648to energize omnigraph magnet 55! and start the operation of omnigraphtransmitter 650 to send over line BIB a line feed code combinationcomprising one spacing, one marking and three spacing signals. The.omnigraph transmitter 656 comprises two cams 652 and 653 which contactwith contact levers 654 and 655, respectively. Cams 652 and 653 areconnected together mechanically and electrically and are frictionallydriven at a speed corresponding to the speed of operation of con-' 653contacts with contact lever 655 immediately after it starts rotation.Contact lever 655 is connected to line 610 by wire 6H5 and contact lever654 is connected through a resistance 65? to ground 658. When contactlever 655 is operated it closes contacts 660 and opens contacts 6M.Opening of contacts 614 disconnects printer or perforator receivingmagnet 6 l2 from line 6 Iii. Contacts 66! which close before contactsGit are opened preserve an energizing circuit for the receiving printeror perforator magnet 6l2 from ground 66! and battery 662, contacts 6%,wire 6|5', magnet (H2 and ground 6l3. Since magnet (H2 is cut off fromthe line during the transmission of the answerback signal from omnigraph650, the answerback signal will not be recorded on the receivingapparatus at this distant end of the circuit, and since it is notrecorded on the record medium used for retransmission of the receivedmessage only the carriage return and blank code combinations appearingat the end of the message can be transmitted to further circuits. If theanswerback line feed code combination were recorded in the perforatedtape record medium at this time it would be added to the carriage returnblank code combinations and cause a false start signal to be transmittedwhen the record medium passes through a retransmitter, as in thepreviously described applications of the method of controllingtransmission from the transmitting station by answerback signalstransmitted by the receiving station under control of message endsignals. The answerback signals are not recorded at the station fromwhich they are transmitted.

To give an alarm at the transmitting station when, due to incorrect ornon-reception of a message at the receiving station, an answerbacksignal is not received at the transmitting station, I have provided aslow release relay 616 and alarm apparatus 6'. 'Slow release relay cm isenergized over closed normally engaged contacts- 633 of relay 630. Whenrelay 630 is operated by the message end signals, it locks up overcontacts Gill and 622. If the answerback signal is not received to opencontacts 622, contacts 633 remain open and after a time interval relay610 will release its armature to close alarm contacts 612 and alarm 61!is operated to call an attendant who will repair any existing fault andrestart transmission.

High frequency answerback system Afurther method of automaticallysupervising aduplexed transmission system by answerback signals is shownin Figure 14, Sheet 6. In this arrangement answerback signals ofrelative high frequency, which are separated from message transmissionsignals by inductive and filter devices, are used. Referring to Figure14, multiplex distributor 100 is shown equipped with transmitting andreceiving connections for one operating channel. Transmitting segments10! are connected to armature levers 102 of transmitting relays 103.Armature levers 102 connect either positive battery 104 or negativebattery 105 to transmitting segments 10| in accordance with theselective setting of relays 103. Brushes I06 connect segments 101 toring 101 and impulses are transmitted from ground 108 through receivingrelay 109 to line 110. Transmitting contacts N of a standard tapetransmitter 116 are set in accordance with the perforations in a tape,to selectively energize relays 103. Brushes 1l1 connect segment 118 toring 120, connected to positive battery, after brushes 106 have passedover segments closing a circuit through perforator operating magnet 12!and relay 122, contacts 123 to negative battery. Receiving segments 130are connected through selecting magnets 131 to relays 132 which areconnected to negative battery. Brushes 133 connect segments I30 to ring134 which is connected to contact 135 ofrelay 109. The armature of relay109 is connected to positive battery. Selecting magnets 13! and relays132 are set in accordance with impulses received by relay 100 whilebrushes 133 pass over segments 130. Brushes 140 connect segment 14| toring 142, connected to positive battery, after brushes 133 have passedover segments 130 to close a circuit through printer or perforatoroperating magnet 143 and break relay 144 to negative battery. Operatingmagnet 143 when energized records the selections made by magnets 131 ona printer or in a perforated tape in a manner well known in the art.

At the distant end of line 110 a like distributor 150 is represented bybox 151 containing the sending equipment, and is connected totransmitting battery and ground. Box 152 connected to contact 155 ofrelay 156 and negative battery contains the receiving equipment. All ofthe sending and receiving equipment is the same as described inconnection with distributor 100 with the exception that the answerbacksending and receiving devices are shown separately.

During message transmission, signal combinations set by tape transmitter1l6 are transmitted to relay 156 and recorded on the receiving apparatusat box 152 and signal combinations from the transmitter at box 151 arereceived by relay 109 and recorded on receiving apparatus shown atdistributor 100, as explained. When the end message combinationcomprising a carriage return code combination followed by a blank codecombination passes through transmitting relays 103,.the carriage returnrow of series contacts.

160 will close and slow release relay 16! will be energized. Thefollowing blank combination will close series contacts 162 and close acircuit from positive battery through contacts 163, contacts 162,contacts 164 of relay 165, contacts 168 and relay 161 to negativebattery. Relay 16! remains operated until contacts 164 are opened by theanswerbaok signal. Contacts 161 close to connect relay 165 to line H0through circuit which includes condenser 111, filter 112, ampli-- fier113, and rectifier 114. Contacts 123 open the circuit from negativebattery to relay 122 and transmitter operating magnet 12!. Magnet 12land relay 122 now remain unoperated when brushes 111 contact withsegment 118 and the blank selection remains set in relays 103. Con tacts116 open the circuit to slow release alarm relay 111.

The circuits are now set to receive the answerback signal which will betransmitted to line 1|0 through condenser 180, from transformer 10!which produces a relatively high frequency of A value, when contacts 182are closed. The arrangement for closing contacts 182 at distributor 150will be understood from the following explanation of the samearrangement used for closing contacts 185 which when closed connecttransformer 166 to line 110 at distributor 100.

Message and message end signals are received :on relays 132 which lookup when operated through contacts I90 included in a circuit frompositive battery contacts 191 of relay 192, contacts 1910, relays 132and negative battery. When brushes 140 connect positive battery tosegment 141 magnets 143 and 144 are energized and relay 141i closescontacts 193 to connect battery 194 in series with condenser chargingthe latter. When brushes leave segment 14!, relay 144 is de-energized,contacts 193 are closed and condenser 195 discharges through relay 192which then opens contacts 191 to release the selecting relays 132. Whenthe message end signal cornbinations are received on relays 132 thecarriage return combination closes series contacts 060 and slow releaserelay 801 is energized when relay I44r is operated. The following blankcombination closes series contacts 802 closing a circuit, when relay 144is operated, from positive battery contacts 803, contacts 802, relay804, contacts 605, relay 80] and negative battery. Relay 804 attractshook lever 806 to release sending cam 801, which is driven at a slowrate of speed by any desirable means, for one revolution during which itdepresses contact lever 308 to close contacts 185 which connecttransformer 166 from ground to line 1E0 through condenser 810.Transformer 186 produces a relatively high frequency of B value.

I have left the transmitting apparatus at distributor 100 in stoppedcondition awaiting an answerback signal from the receiving apparatus atdistributor 150. This, when the message end signal is received, will besent from transformer 181 on the closing of contacts 182 and receivedthrough filter 112 which passes the A frequency and rejects the Bfrequency then through amp1ifier 113 and rectifier 114 and relay whichis operated to open contacts 164 releasing slow release relay 161 whichcloses the transmitter operating circuit through contacts 123 to restartmessage transmission. The circuit to slow release alarm relay 111 isagain closed and the high frequency receiving apparatus is disconnectedfrom line 110 at-contacts 161. If through some faultthe messageendsignals are notreceived at 21 distributor 150, contacts 182 will not beclosed and no answerback returned to distributor E60. When this occursslow release relay ll! will after a fixed period release its armatureand a circuit will be closed through contacts tie to operate alarm 8l5which will summon an attendant to correct the existing fault.

Distributor 150 is provided with high frequency receiving apparatusconsisting of filter 828 which passes a relatively high frequency of Bvalue and rejects a frequency of A value, an amplifier 321, a rectifier822 and a relay 823 operating contacts 824 which control the restartingof transmitter 15l. The high frequency receiving apparatus is connectedfrom ground through contacts 825 and condenser 826 to line 1 i ll.

While filters 112 and 820 will effectively differentiate betweenfrequencies in continuous wave form, it is probable that kicks fromreversals of message transmission signals will pass through condener BIBto relay 165. Such kicks would act the same as static in radio receptionand will cause short opening and closing of contacts ltd. The resultingshort breaks in the circuit of relay Nil will have no effect due to theslow release nature of this relay. The continuous application of an Avalue frequency will however open contacts 154 for a suiiiciently longperiod to permit the full de-energization of relay liil so that itsarmature will be released.

From the foregoing it will be seen that I provide a system oftelegraphic communication primarily controlled from a manually operableswitch board, requiring a minimum of manual supervision and having meansfor indicating the ultimate destination address as well as the characterof a particular message being transmitted over a selected trunk line.Also at the switch board means is provided to prevent removal of thetrunk line plug from the jack during transmission of a message, withmeans for automatically disconnecting the plug when the message iscorrectly transmitted to the receiving station; and means to prevent theconnection of the plug to a busy circuit.

My invention further includes the novel feature of transmittinganswerback signals from the receiving station to the transmittingapparatus under control of a message end signal after the message isreceived at the receiving station, together with means for disabling thecircuits and operating a trouble alarm in the event that the answerbacksignals are not correctly received. Also when the message includesfigures or punctuations recorded in the shifted position of the messagecharacter recorder, means automatically operates to prevent registrationof the answerback or service signals and the recording in the message ofunshifted signal combinations, which may be included therewith.

Another desirable feature of the invention herein disclosed is thatwhen, owing to some operational fault in the system, the answerbacksignal arrives at the receiving station in the body of the message, themessage transmitting functions of the apparatus are automaticallydisabled until the fault is corrected.

Other novel features of the invention as heretofore described includethe transmitter having means for automatically controlling operatingcircuits for the switch board indicators which apprise the attendant ofthe ultimate destination of the message being transmitted, as well aswhether the message is one of an ordinary, deferredor urgent character.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the

scope of the invention being indicated by the signal transmitting andreceiving apparatus, said.

transmitting apparatus including means to transmit a variable group ofword signals and message end signals; and means responsive to the.transmission of a message end signal to automatically disable thetransmitting apparatus and prevent the further transmission of messagesand means controlled by the receiving apparatus and automaticallyresponsive to the reception of a message end signal to condition thetransmitting apparatus for message transmission.

2. In a system of telegraphic communication, signal transmitting andreceiving apparatus, said transmitting apparatus including means totransmit a variable group of word signals and message end signals; andmeans responsive to the transmission of a message end signal toautomatically disable the transmitting apparatus and prevent the furthertransmission of messages and means controlled by the receiving apparatusand automatically responsive only to the correct interpretation andreception of a message end signal to condition the transmittingapparatus for,

message transmission.

3. In a system of telegraphic communication having transmittingapparatus connected to incoming lines, receiving apparatus connected tooutgoing lines and switching means for selectively connecting theincoming and outgoing lines; means for transmitting a message whichincludes an address portion, a message portion and a message endindicating portion from the transmitting apparatus to the receivingapparatus, means responsive to signals indicating the message end todisable the transmitting apparatus, answerback message sending devicesat the receiving apparatus, and means also controlled by the message endsignals to first operate said devices and to thereafter condition themessage transmitting apparatus for message transmission.

4. In a system of telegraphic communication having transmittingapparatus connected to incoming lines, receiving apparatus connected tooutgoing lines and switching means for selectively connecting theincoming and outgoing lines; means for transmitting a message whichincludes an address portion, a message portion and a message endindicating portion from the transmitting apparatus to the receivingapparatus, means responsive to signals indicating the message end todisable the transmitting apparatus, answerback message sending devicesat the receiving apparatus, and means also controlled by the message endsignals to first operate said devices and to thereafter condition themessage transmitting apparatus for message transmission, an alarm deviceat the transmitting apparatus, and means automatically responsive, inthe event of non-reception of an answerback message after transmissionof the message end indicating signals, to operate said alarm device.

5. In' asystem of telegraphic communication;

board, and said transmitting apparatus including means for controllingoperation of said message destination and classification indicatingmeans; means for transmitting a message which includes an addressportion, a messageportion and a mes,- sage end indicating portion fromthe transmitting apparatus to the receiving apparatus, means responsiveto signals indicating the message end to disable the transmittingapparatus, answerbaok message sending devices at the receiving appara-.tus, and means also controlled by the message end signals to firstoperate said devices and to thereafter condition the transmittingapparatus for message transmission.

6. In a system of telegraphic communication having transmittingapparatus connected'to incoming lines, receiving apparatus connected tooutgoing lines, a switchboard, switching means on said board forconnecting an incoming to an outgoing line, a key on said board to starttransmission over the outgoing line, message destination andclassification indicating means on said board, and said transmittingapparatusincluding means for controlling operation of said messagedestination and classification indicating means; means for transmittinga message which includes an address portion, a message portion and amessage end indicating portion from the transmitting apparatus to thereceiving apparatus, means responsive to signals indicating themessageend to disable the transmitting apparatus, ,answerback message sendingdevices at the receiving apparatus, and means also controlled by themessage end signals to first operate said devices and to thereaftercondition the transmitting apparatus for message transmission; and meansauto matically operative after complete reception of a transmittedmessage by the receiving apparatusto actuate said switching means anddisconnect the outgoing line from the incoming line.

7. In a system of telegraphic communication having transmittingapparatus connected to incoming lines, receiving apparatus connected tooutgoing lines, a switchboard, switching means on said board forconnecting an incoming to an outgoing line, a key on said board to starttransmission over the outgoing line-message destination andclassification indicating means on said board, and said transmittingapparatus including means for controlling operation of saidmessagedestination and classification indicating means; means for transmittinga message which includes an address portion, a message portion and amessage end indicating portion from the transmitting apparatus to thereceiving apparatus, means responsive to signals indicating the messageend to disable the transmitting apparatus, answerbacl: message sendingdevices at the receiving apparatus, and means :also controlled by themessage end signals-to first operate said devices and to thereaftercondition the transmitting apparatus for message transmission;additional indicating devices on said board, respectively operative toindicate transmission and non-reception of a message, also operativelycontrolled by said transmission apparatus; and

means automatically operative after complete reception of a transmittedmessage by -the-receiv- 24 1 ing apparatus to actuate said switchingmeans and disconnect the outgoing line from the incoming line.

8. In a system for transmitting telegraph messages, a plurality ofincoming and outgoing circuits, switch means to selectively interconnectindividual circuits of said plurality of incoming and outgoing circuitswith each other to transmit a message thereover which comprises anaddress portion, a message portion and a message end indicating portion;means associated with the switch meansto control the transmission of sinals indicating the address and message end portions of the message, andmeans controlled by the signal control means for the message endindicating portion to stop further transmission from the incomingcircuit while maintaining the interconnection between said incoming andoutgoing circuits.

9. In a system for transmitting telegraph messages, a plurality ofincoming and outgoing circuits, switch means to selectively interconnectindividual circuits oi said plurality of incoming and outgoing circuitswith each other to transmit a message thereover which comprises anaddress portion, a message portion and a message end indicating portion;means associated with the switch means to control the transmissionofsignals indicating the address and message end portions of the message,means controlled by the signal control means for the message endindicating portion to stop further transmission from the incomingcircuit while maintaining the interconnection between said incoming andoutgoing circuits; and additional signal controlled means responsiveonly to the prior transmission of a message end signal to automaticallydisconnect the incoming and outgoing circuits at the switch means.

10. In a system for transmitting telegraph messages having a pluralityof incoming and outgoing circuits, transmitting and receiving apparatusand means for selectively inter-connecting individual incoming andoutgoing circuits, said transmitting apparatus including means totransmit message end signals; means controlling the transmittingfunctions of said transmitting apparatus, means operatively responsiveto the effective operation of said message end signal transmitting meansto stop operation of said control means and render the transmittingapparatus inoperative to transmit further messages; and meansautomatically responsive to the reception of a message end signal by thereceiving apparatus to condition said controlling means and again rendersaid transmitting apparatus operative for the transmission of messages.

11. In a system for transmitting telegraph messages having a pluralityof incoming and outgoing circuits, transmitting and receiving apparatusand means for selectively inter-connecting individual incoming andoutgoing circuits, said transmitting apparatus including means totransmit message end singals; means controlling the transmittingfunctions of said transmitting apparatus, operatively responsive to theefiective operation of said message end signal transmitting means, torender the transmitting apparatus inoperative to transmit furthermessages; answerback message sending devices at the receiving apparatus,means controlled by the message end signal transmitting means to operatesaiddevices and to condition said first-named controlling means to againrender said transmitting; apparatus operative for thetransmissionoimessages,

and means to prevent the recording of answerback signals at the lastnamed receiving apparatus.

12. In a system for transmitting telegraph messages having a pluralityof incoming and outgoing circuits, transmitting and receiving apparatusand means for selectively inter-connecting individual incoming andoutgoing circuits, said transmitting apparatus including means totransmit message end signals; means controlling the transmittingfunctions of said transmitting apparatus, operatively responsive to theeffective operation of said message end signal transmitting means, torender the transmitting apparatus inoperative to transmit furthermessages; an-

swerback message sending devices at the receiving apparatus, and meanscontrolled by the message end signal transmitting means to operate saiddevices and to condition said first-named controlling means to againrender said transmitting apparatus operative for the transmission ofmessages; and additional means automatically controlled by said messageend signalling means, after transmission of the message end signal, andcooperating with said interconnecting means to disconnect said incomingand outgoing circuits.

13. In a system for transmitting telegraph messages having a pluralityof incoming and outgoing circuits, transmitting and receiving apparatusand means for selectively inter-connecting individual incoming andoutgoing circuits, said transmitting apparatus including means totransmit message end signals; means controlling the transmittingfunctions of said transmitting apparatus, operatively responsive to theefiective operation of said message end signal transmitting means, torender the transmitting apparatus inoperative to transmit furthermessages; answerback message sending devices at the receiving apparatus,and means controlled by the message end signal transmitting means tooperate said devices and to condition said first-named controlling meansto again render said transmitting apparatus operative for thetransmission of messages; additional means automatically controlled bysaid message end signalling means, after transmission of the message endsignal, and cooperating with said interconnecting means to disconnectsaid incoming and outgoing circuits; and means to prevent effectiveoperation of said last-named means by an answerback signal at any othertime than after the complete transmission of a message.

14. In a system of telegraphic communication having transmittingapparatus connected to an incoming line and receiving apparatusconnected to outgoing lines; a switchboard, jacks on said boardconnected with the transmitting apparatus, trunk line plugs forselective connection with said jacks in accordance with messageaddresses, locking means to retain the plugs in connected relation withthe jacks and means effective to render the locking means inoperativewhen more than one trunk line plug is connected With said jacks at thesame time.

15. In a system of telegraphic communication having transmittingapparatus including a permutation code transmitter connected to incominglines and printing telegraph receiving apparatus connected to outgoinglines; a switchboard, jacks on said board connected with thetransmitting apparatus, trunk line plugs for selective connection withsaid jacks in accordance with message addresses, means operativelycontrolled by a start key for retaining said plugs in locked. connectionwith the jacks during message transmission, and means automaticallycontrolled by the permutation code transmission apparatus to actuatesaid locking means upon completion of message transmission and releasethe plug for disconnection from the jack.

16. In a system of telegraphic communication having transmittingapparatus connected to an incoming line and receiving apparatusconnected to outgoing lines; a switchboard, jacks on said boardconnected With the transmitting apparatus, trunk line plugs forselective connection with said jacks in accordance with messageaddresses, means for locking the plugs in connected relation with thejacks and means operatively controlled by the individual plugs toprevent the efiective operation of said locking means when more than oneplug is connected to the same circuit.

1'7. In a system of telegraphic communication having transmittingapparatus connected to an incoming line and receiving apparatusconnected to outgoing lines; a switchboard, jacks on said boardconnected with the transmitting apparatus, trunk line plugs forselective connection with said jacks in accordance with messageaddresses, means operatively controlled by the individual plugs toprevent the effective connection of more than one trunk line plug withsaid jacks at the,

same time, said last-named means including look-'- ing devices for theindividual plugs associated with the respective jacks, meansautomatically operative when more than one plug is inserted in the jacksat the same time to prevent effec-p tive operation of said lockingdevices, and means for ejecting the inserted plugs from the jacks.

18. In a system of telegraphic communication having transmittingapparatus connected to an incoming line and receiving apparatusconnected to outgoing lines; a switchboard, jacks on said boardconnected with the transmitting apparatus,

trunk line plugs for selective connection with said jacks in accordancewith message addresses; means operatively controlled by the individualplugs to prevent the effective connection of more than one trunk lineplug with said jacks at the same time, said last-named means includinglooking devices for the individual plugs associated with the respectivejacks, means automatically, operative when more than one plug isinserted in the jacks at the same time to prevent effective operation ofsaid locking devices, means for ejecting the inserted plugs from thejacks, and

means automatically controlled by the transmission apparatus to causeactuation of an individual locking device upon completion of messagetransmission and the disconnection of the trunk line plug from theassociated jack by said ejecting means.

19. In a system of telegraphic communication having transmittingapparatus connected to incoming lines, receiving apparatus connected tooutgoing lines and switching means for selectively connecting theincoming and outgoing lines; means controlling transmission of messagesignals over a transmission channel from the transmitting to thereceiving apparatus, means at the receiving apparatus for transmittingan answerback signal over a channel carrying message signals differingin character from those carried by said transmitting channel and meansoperatively dependent upon operation of said last-named means todiscontinue transmission of message signals over said last named channelduring transmission of the answerback signal.

20. In a system of telegraphic communication having transmittingapparatus connected to" incoming lines, receiving apparatus connected toanswerback signal over a sending channel, means operatively dependentupon operation of said last-named means to discontinue transmission ofmessage signals over said transmission channel during transmission ofthe answerback signal; means at the transmitting apparatus for recordinganswerback codes ignal combinations, and means for selectivelydifferentiating between different code combinations, operative toprevent recording of the selected combination without affectingtransmission thereof over the associated sending channel.

21. In a system of telegraphic communication, signal conducting means,sending and receiving apparatus at each of two stations, means totransmit messages in two directions simultaneously and means associatedwith the receiving appa ratus at each station to automatically transmitsignals to control the transmission of message signals in one directionby the sending apparatus at a station to said receiving apparatus at theother station over said signal conducting means including means tointerpose such controlling signals'with message signals transmitted inthe opposite direction.

22. In a system of telegraphic communication, message transmittingapparatus and message receiving apparatus, said transmitting apparatusadapted to transmit messages to the receiving apparatus in permutationcode including a message end portion comprising a plurality ofpermutation code combinations, means responsively controlled bytransmission of said message" end indicating portion of the message tostop message transmission, and means to restart message transmission,including means associated with the receiving apparatus andresponsive tothe reception thereby -of said message endindicating portion to transmita single one of said message" end permutation code combinations to thetransmitting station to condition said transmitting apparatus to restartmessage transmission.

23. In a method of telegraphic communication between sending andreceiving stations, establishing a message transmission connectionbetween said stations, transmitting an end of message indicating signalafter-transmission of a message and then stopping further transmissionwhile maintaining said established connection; interpreting thetransmitted message at the receiving station and, in response to correctreception ofsaid message end indicating signal, disestablishing themessage transmission connection between said stations.

24. In a system of telegraphic communication in which message charactersare transmitted and received in permutation code combinations and inwhich characters are recorded in the shifted and unshifted positions ofcharacter receiving apparatus under control of transmitted shift andunshift code combinations, said system including means to transmitandreceiveanswerback or service signals comprising shift, service andunshift code combinations; means automatically operative during messagetransmission to inter-- pose such answerback or service signals, andmeans associated with the character receiving ap- 28 paratus"toselectivelydi'scard such service or answerback code combinations aswould alter the construction of a transmitted message.

25. In a. system of'telegraphic communication in which messagecharacters are transmitted and received in permutation code signalcombinations and in which characters are recorded in the shifted andunshifted positions of character receiving apparatus under control ofshift and unshift-code combinations; service and answerback devices at atransmitting station, means to transmit to said devices at all times,service and answerback signals from a receiving to a transmittingstation, said signals including shift, service and unshift codecombinations, and means associated with said receiving apparatus toprevent the recording of the unshift portion of such service oranswerback signal combinations in the character receiving apparatus whenthe receiving apparatus is positioned to print characters in the shiftedposition.

26. In a system of telegraphic communication in which messages aretransmitted in permutation code combinations to message characterreceiving apparatus, answerback and service indicating devices at asending station, means to transmit service or answerback signals from areceiving to a sending station to operate said devices at all times,said signals comprising shift, service and unshift code combinations,and means associated with the receiving apparatus at said receivingstation to cancel the recording of such service oranswerback signalcombinations in the said message character receiving apparatus.

27. A system of telegraphic communication including means by whichmessage characters are transmitted and received in permutation signalcode combinations and in which two of such signal combinations are usedto indicate the end of a message, and means'for difierentiallydistinguishing the efiective'operation of such tWo' code signalcombinations when used in the body of a message from their efiectiveoperation when used to indicate the end of a message.

28. In .a communication system, means for transmitting message signalsfrom a sending station to "be recorded at a receiving station atpermutation code frequency, means for transmitting and receiving servicesignals'at service impulse frequency, and means at said sending andreceiv ing stations to automatically differentiate between said messageand service impulse frequencies and prevent recording of service signalimpulses with the permutation code message signa s;

29. In a communication system for transmitting messages from a sendingto a receiving station, meansfor transmitting an end-of-message signalto the receiving station at permutation code frequency, means at thesending station for restarting transmission of messages, high frequencysignal transmission means at the receiving station controlling saidrestarting means, said high frequency transmitting means being normallydisconnected from the transmission means at both the transmitting andreceiving stations and means operativel controlled by saidend-of-message signal to connect the high frequency transmitting andreceiving means to the transmission means at both stations, and means tostop further transmission of messages from the sending station andenergize said high frequency signal transmission-means to operate saidrestarting means and restart the transmission of messages.

